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restorative section

FIG 1: MDP Monomer – chemical structure FIG 2: Successive layers between dentin and zirconia surface in MDP cementation

3. Chloro- Silane treatment ditioning agent.
Chloro-silane treatment is introduced earlier as a pre- treatment of
zirconia surfaces. Chloro-silane combined with vapor phase tech- 5. Laser application
nique allowed pretreatment that deposits a silica-like layer on the Er:YAG (erbium-doped yttrium aluminum garnet) laser has the
zirconia substrate. The result is very thin coating (till 2.6 nm) which ability to remove particles through ablation process by micro-explo-
increased the number of chemical binding sites (SixOy) for the sub- sions and vaporization. Laser effects obtained due to temperature
sequent organ-saline primer, used in conventional adhesive tech- changes (heating and cooling), induce phase transformation in the
nique. Application of the Chloro-silane film increases the bond material leading to its damage. It has been suggested to lower the
strength to resin cements enabling the values of laser power and to enable surface irradiation with con-
microtensile bond strength similar to clinically com- stant water cooling. But, the results are still question-
mon bonding technique able regarding the fact that laser irradiation is not as
effective in increasing bond strength as air-particle
4. Selective infiltration etching [SIE] abrasion under in vitro experiments.
Though zirconia has been very commonly called as Other processes that have been developed and tried
white metal, and macroscopically it exhibits a very are namely Gas phase fluorination process, Zirconia
smooth, hard inert surface [which makes it quite dif- ceramic powder coating, Nonstructured alumina parti-
ficult for GIC cements to provide good adhesion, dis- cle coating, silica coatings etc
used later]. At microscopic nano scale zirconia
exhibits a dynamic structure due to changing grain RELIABLE TECHNIQUES
boundaries, resulting from the transformation phases. Literature shows that the most reliable method of
The flux grain boundaries can allow infiltration of cementation of Zirconia is the use of resin cements.
various elements. The technique utilises this property Three methods are the mainstay of Zirconia bonding
of zirconia. Surface of zirconia is coated with a glass- with resin cements:
containing conditioning agent silica (65% wt.), alu- 1. The first method recommends a ceramic primer
mina (15% wt.), sodium oxide (10% wt.), potassium or resin cement, which contains a bio-functional
oxide (5% wt.) and titanium oxide (5% wt.) with monomer, 10- methacryloyloxydecyldihydrogen-
closely-matched thermal expansion coefficient to zir- FIG 3: Monobond Plus Refill phosphate (MDP). This monomer has the same basic
conia. Later on, the material is heated above glass chemical structure as any primer or bonding M-R-X,
transition temperature, until the optimal grain where M represents a methacryl group and its role is to
boundary diffusion is achieved. After cooling to room temperature, copolymerize with resin matrix, R is a different length hydrocarbon
the glass is dissolved in an acidic bath to eliminate all traces of con- chain with spacer function and X is an acidic phosphate group and

26 Dental Practice // January-February 2021 // Vol 17 No 4 Continued on page 28 >>